[font color=\'#000000\']I had a discussion with a buddy who has one on his newly acquired 20D, so this is third-party info --
His initial impressions were it was about equal to the 28-135 IS on a full-frame camera, yet it vignettes significantly (I think his word was "horrible") at the wide end on the 20D. He confirmed this vignetting was NOT due to the UV filter he had mounted.
That being said, he liked it as a lightweight travel lens for that camera, but put it the "snapshot" category.[/font]